1. Field of the Invention
This invention relates generally to raceways for current-carrying conductors, and more particularly to a divider for separating current-carrying conductors in a raceway for cooling.
2. Description of the Related Art
It is known to use protective sheathing, such as metal or plastic conduit, to enclose a current-carrying conductor that extends through walls, ceilings and floors between a receptacle and a circuit panel. Conduit is used to protect the conductor from heat, abrasion and impact that could burn, wear or cut through the insulation layer on the exterior of the conductor. If the insulation layer is breached, the conductor is likely to short circuit through another conductor, such as another wire, a circuit panel or a person.
It is also known to enclose multiple conductors in raceways that can also be enclosed within the walls, ceilings and floors of buildings, in addition to extending along open walls of commercial and industrial buildings, in ducts (e.g., walker ducts) in the floors of such buildings and within underground ducts. By extending multiple conductors through the same raceway, many conductors can be enclosed by a single protective cover, thereby saving material and labor costs in constructing the electrical connections. Such large raceways also permit the addition of conductors after the original construction, thereby saving on the costs of future expansion.
Individual conductors generate heat according to known principles of physics, but single conductors can generally cool fast enough by exposure to air around the conductor to prevent significant thermal breakdown of the insulation. However, when many conductors are crowded into a raceway and seat against one another, the heat generated cannot be removed rapidly enough. The temperature can increase enough to cause thermal breakdown of the insulation. Therefore, electrical codes place limitations on the number of conductors that can be placed in raceways to prevent such thermal breakdown. However, these codes often restrict the number of conductors in a raceway to a small portion of the vacant space in a raceway. For example, ratings dictate how many wires can be in a raceway of a particular size and capacity. Some ratings require that raceways be only 20 percent full or contain no more than 30 current-carrying conductors.
In order to avoid losing space that otherwise goes unused, electrical contractors, especially those who are adding conductors to an existing raceway, place objects between the conductors to space the conductors and permit cooling by air circulation. Typical of such objects include blocks of wood (although combustible materials are not generally permitted in raceways), wire ties screwed to a sidewall of the raceway and similar structures that are not convenient, efficient or safe. The prior art includes other devices that attempt to create spaces between the conductors. However, the prior art devices have disadvantages that make them undesirable.
U.S. Pat. No. 4,962,639 to Blase discloses a multi-passage subdivider for chain links. Space is formed around the wires by dove-tailed partition walls that are especially designed for particular positions. The sizes and shapes of the components and compartments vary.
U.S. Pat. No. 6,706,969 to Young discloses a cable spacing device for low voltage cables that is limited to a few rows of divided wire passages. Additionally, the dividers can be inserted in only one end of the device, thereby making it applicable for very few conductor raceways.
U.S. Pat. No. 4,570,883 to Wepfer discloses a very complex arrangement of plates for separating spaced tubes. The emphasis in this structure is on the resilient parts of the supports, and the device is not modular in the same direction as the tubes, but in the direction that is perpendicular to the orientation of the tubes. This prevents the addition of more spacers after the tubes are in place.
Therefore, the need exists for a raceway divider that permits cooling of the conductors placed therein, that is readily installed in virtually any conductor raceway, and that can be installed in existing raceways with conductors.